This project addresses issues related to cochlear implantation using audiological and speech-perception techniques. We will perform experiments that should expand selection criteria and improve performance. First, we will implant adults with more residual hearing to determine if the current selection criteria can be broadened to benefit more patients. Second, three different experiments will test opportunities to improve speech perception and music by novel speech-processing approaches. We will use a high-rate conditioning processor to produce more natural nerve-fiber activity. A short electrode will be inserted in patients with good low- frequency hearing, and then the ear will be stimulated with combined acoustical and electrical signals. Some patients will also receive binaural implants, and studies with independent processors will attempt to improve the binaural advantage for localization and speech perception in noise. The Electrophysiology Project will assist in fitting and the Music Project will assist in the evaluation of these studies. Third, many of our patients are older and can be expected to experience cognitive difficulties. However, hair-cell loss due to aging will not affect these patients, so their performance may not deteriorate as occurs in adults with hearing aids. More children are being identified early with hearing loss, and accurate measures are needed to determine behavioral thresholds in children before 12 months of age. A computer-based visual reinforcement audiometry system will be used to measure a head-turn response, and these same children will be tested later with play audiometry using the exact same equipment. Parallel measures will be made by the Electrophysiology Project. In our effort to further define appropriate selection criteria in children, we will work with the Language Project to determine if the advantage afforded by early implantation extends down to children 12 months of age. To further explore which children should get cochlear implants and which should get hearing aids, we will also measure the speech perception of hearing-impaired school-aged children using well-fit hearing aids. Fifth, we will evaluate children who have been using their implants for many years to document the levels of benefit that can be expected and the factors that contribute to success.